SYDNEY,:Four children were killed and several more badly injured in Australia after strong winds lifted an inflated jumping castle into the air during end-of-year school celebrations, causing them to fall 10 metres (33 feet), authorities said on Thursday, prompting an outpouring of grief.

Two boys and two girls in their final year of primary school died in the accident in Devonport, in the northwest of Tasmania state, about 10 a.m. (2300 GMT on Wednesday). Five more children were in hospital, four in critical condition, authorities said.

There was no immediate explanation for how the jumping castle became airborne, and no other details were released of the children's identities except that the incident took place at Hillcrest Primary School. Students in the last year of primary school, Year 6, are typically aged 10 or 11.

The accident would rank among Australia's deadliest involving an amusement ride, and brought on a wave of disbelief and mourning.

"On a day when these children were meant to be celebrating their last day of primary school, instead we're all mourning their loss," Tasmania Police Commissioner Darren Hine told reporters.

"Our hearts are breaking for the families and the loved ones, schoolmates, teachers of these young people who were taken too soon.

Tasmanian premier Peter Gutwein said "it is simply inconceivable that this shocking tragedy has occurred" and promised a thorough investigation.

Prime Minister Scott Morrison described the incident as "shattering and heartbreaking".

"Young children on a fun day out, together with their families and it turns to such horrific tragedy at this time of year. It just breaks your heart," Morrison told reporters.

Hine, the police commissioner, said after an initial investigation the accident would be referred to a coroner for an inquest.